Glass has been widely used as a substrate for a display device such as a liquid crystal display device and an organic EL display device, a substrate for a color filter, a substrate for a solar cell, and the like. In recent years, however, a plastic material is being considered as a substitute for a glass substrate owing to such reasons that the glass substrate is liable to fracture, cannot be bent, is not suitable for reduction in weight due to the large specific gravity thereof, and the like. For example, substrates made of polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyolefin and polyethersulfone are proposed (for example, in JP-A-2007-268711, Patent Document 1).
It has been disclosed that though these conventional plastic materials as a substitute for glass have a larger linear coefficient of thermal expansion compared to glass, the linear coefficient of thermal expansion can be reduced by dispersing tabular inorganic substance in a plastic material (e.g. JP-A-2008-45121; Patent Document 2 (WO 2008/010610)).
Conventionally, in plastic substrates for a display, a transparent electrode on the substrate is formed by forming a film of an oxide of a metal such as indium and tin on plastic in vacuum by a method such as argon sputtering and ion plating. In that case, a high degree of vacuum is required for forming a film of the metal oxide from an evaporation source of the metal oxide on the surface of the plastic uniformly. Also, to obtain an oxide film having a low resistance value, it is necessary to raise the substrate to high temperature to thereby attain high crystallinity degree of the oxide film.
However, these conventional plastic materials as a substitute for glass have had a problem that unreacted monomer and other low-molecular-weight components vaporizes from the inside of the material upon the vapor deposition of a conductive thin film on the material surface at high temperature and under vacuum, which leads to a lower degree of vacuum in the vapor deposition apparatus and inhibits normal deposition. Hence, a plastic material containing a small amount of volatile components has been demanded.